I like the story of the marmorkrebs, a kind of crayfish that reproduces pathogenetically. Because of this, they’re genetically identical, so all of the many phenotypic differences seen between them must be due to environmental factors. Except that they aren’t: Controlling for the environment to the extent possible, they still exhibit an astounding variety in form and behavior.
It’s a great example illustrating real-world randomness. I heard about it a few years ago on an episode of the podcast Econtalk. Host Russ Roberts was interviewing writer Michael Blastland:
Here’s a way of understanding that old thorny question about the balance of forces between nature and nurture. Because we’ve got half the problem contained. It’s absolutely nailed down: They’re genetically identical. So, if we see differences in these creatures, well, it’s got to be the other one. It’s got to be the environmental cause in that case.
So, [the scientists] got hold of a few of these things, and they started putting them into tanks in the lab. But they also went a step further, and this is where it gets really interesting, because they also standardized their environments. They made sure that the water every single creature was in was the same. They made sure that all their food was the same; they made sure that every single creature had more than enough to eat so there needn’t to be any competition for food. They put quite a lot of them on their own so there wasn’t even any interaction. They had the same person examine them on every occasion using the same variety of rubber gloves. They tried basically to standardize everything they could think of and make their environments as boringly uniform as imaginable. And, this is Germany – they’re good at that.
So, what did they look like, these creatures, as they developed? Because, now we have perfectly consistent genetics: they checked that, they didn’t just assume it. We have, as far as humanly possible, a consistent environment. These are the big-two causes as far as we know of everything. The marmorkrebs – you know where this is going – they’re fantastically varied. You can take marmorkrebs from the same batch of eggs and one of them turns out 20 times the weight of another. The physical variety is just astonishing.
They’re genetically identical, their environments are identical. They’re all fed to excess – no competition for food. One is 20 times the weight of another. The carapace on every single one of them, the shell, has a different pattern of markings […]
So, they’re physically different. They’re also behaviorally different. Some of them like a crowd, some of them are loners. Some of them were really gregarious. Some of them are dominant. When you bring them together, some of them turned out to be dominant and some of them are kind of subservient. Some of them feed when they’re laying, some of them don’t. The point in life when they start laying eggs is quite radically different. Their lifespans vary by a factor of three.
[…] Here are two of the most Herculean regularities we’ve ever come across, genetics and environment. And, it’s neither.
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